Collins started his career in the Welsh leagues with Mold Alexandra and Buckley Town before joining Chester City in 1996. His first two seasons at Chester saw him make 20 appearances, during the 2002–03 season he went on loan to non-league side Vauxhall Motors. Following his return to Chester, Collins became a regular in the side and produced some fine performances which attracted the attention of Sunderland who brought him for £140,000. Collins spent five years in the North East making over 150 appearances and earning two promotions to the Premier League during that time. In August 2009 Collins joined Stoke City for £2.75 million and played at left back for the "Potters". After losing his place in the squad he joined Ipswich Town on loan in September 2011 and then West Ham United in March 2012. He signed for Nottingham Forest in July 2012.

Collins made his debut for Chester in a 3–1 defeat against Northwich Victoria on boxing day 2001.[4] In just under three years he made over 70 appearances for Chester. It was after a successful spell on loan at Vauxhall Motors that his career started to take off, having been converted from an unconvincing forward into a composed central defender. His time at Vauxhalls included helping them surprisingly knock Queens Park Rangers out of the FA Cup in November 2002. The following season saw Collins miss just one game as Chester won the Football Conference title and returned to the Football League after a four-year absence. Although Chester had a mixed start to the 2004–05 season, Collins continued to impress and a stoppage time goal against Macclesfield Town gave Chester their first win of the season on 4 September 2004.

A month later he joined Sunderland for £140,000[5] amid interest from other clubs including Sheffield United whose manager Neil Warnock hit out at the way Chester handled his transfer to Sunderland.[6] He ended the 2004–05 season with another championship medal and full Welsh caps to his name, he was initially used as a backup player to defenders Gary Breen, Steven Caldwell and George McCartney, in his first season at the club, but still managed to make 14 appearances. Following promotion to the Premier League for the 2005–06 season, Sunderland signed several additional players and Collins found himself out of the first team squad early in the season. He later worked his way into the side but Sunderland endured a nightmare campaign and were comfortably relegated amassing just 15 points.[7]

Collins started the 2006–07 season as first choice defender at Sunderland, but was dropped four games into the season after being booed by a section of the crowd following a mistake in the previous game against Plymouth Argyle. Collins later regained his place following the arrival of manager Roy Keane and won another championship medal come the end of the season. On 15 December Collins scored a late last minute goal against Aston Villa which would have led to the Black Cats victory but referee Steve Bennett denied the goal for a foul on Scott Carson, the foul was not apparent and the goal should have stood. Manager Roy Keane was very angry at the decision and said that Bennett had cheated Sunderland and went as far as to say "the players deserve better."[8]

On 5 April 2008, Collins scored Sunderland's first goal in their 3–1 over Fulham at Craven Cottage despite again having a goal disallowed earlier in the game. Collins has gone on to firmly establish himself as a first team regular at Sunderland, starting 32 games in the 2007–08 season. On 30 January 2009, Collins was rewarded with a new two-and-a-half year contract by Sunderland, keeping him at the club until at least the end of the 2010–11 season.[9] He won the Fans' Player of the Year award in 2008 and 2009.

On 29 August it was reported that Sunderland had accepted a bid from Stoke City for Collins despite this he was an unused substitute when the two sides played each other the next day[10] As expected he signed for Stoke City on 1 September 2009 for £2.75 million rising to £3.5 million.[11][12] Collins made his Stoke debut in a 2–1 defeat at home to Chelsea[13] in the following match against Bolton Wanderers Stoke were leading up until the 88th minute when Collins fouled Sam Ricketts in the penalty area costing Stoke three points.[14] Collins struggled to establish himself at left back during the 2009–10 season often rotating with Danny Higginbotham.[15]

Collins begun the 2010–11 season in good form and has stated that he needs to keep performing well if he is to hold his left back position."There is a lot of competition here now in every area on the pitch, so the lads who are playing at the moment, like myself, know we have to keep performing. If we don't then there are options there for the manager to change things"[16] However he again struggled and was dropped back to the bench with Higginbotham and Marc Wilson being preferred at left back.[17]

Collins was left out Stoke's 25-man Premier League squad by manager Tony Pulis for the 2011–12 season.[18] Collins joined Ipswich Town on a three-month loan deal from Stoke City on 9 September 2011.[19] He played in 16 Championship matches for Ipswich scoring three goals before returning to Stoke. Collins stated that he expected to leave Stoke in the 2012 January transfer window.[20] He did not secure a transfer away from Stoke and made a rare appearance in the fifth round of the FA Cup away at Crawley Town.[21] He also played against Valencia in the UEFA Europa League at the Estadio Mestalla.[22]

Despite being born in England, Collins has represented Wales at international level.[12][32] He made his debut on 9 February 2005 during a 2–0 win over Hungary in the first match of John Toshack's second spell as Wales' manager.[33] His last cap came on 22 August 2007 during a 1–0 friendly win over Bulgaria. Two months after the match, Collins withdrew from the Wales squad to face Germany and Slovakia in the qualifying round of UEFA Euro 2008.[34] Having previously fallen out with Toshack over being left on the bench during a friendly match with Paraguay in March 2006,[35] Collins had not been called into the Wales squad since 2007.[32] Following the resignation of Toshack and the appointment of Brian Flynn as Wales caretaker manager, Collins was selected in the Wales squad for the UEFA Euro 2012 qualifying matches in October 2010. His first call-up as a Forest player was in the squad to face Belgium and Serbia in the 2014 FIFA World Cup qualifiers. However, Collins turned the call-up down.[28]